1. Field of the Invention
The present invention generally relates to a radiation sensitive composition which is sensitive to radiations. Particularly, it relates to a radiation sensitive composition which is suitable as a resist for the preparation of semiconductor integrated circuits.
2. Discussion of Background
High integration of semiconductor integrated circuits progresses at a speed of four times in three years. For example, in the case of dynamic random access memory (DRAM), production of DRAM having a memory capacity as large as 16M bits has now started on a commercial basis. Accordingly, the requirements for the photolithography technology essential to the production of such integrated circuits have been stricter year after year. For example, for the production of 16M bits DRAM, a lithography technique of 0.5 .mu.m level is required, and for more highly integrated 64M bits DRAM, a lithography technique of 0.35 .mu.m level is required. It is accordingly desired to develop resists which can meet the requirements of the respective lithography levels.
Along with the progress in submicron processing, the wavelength used for exposure of a resist has become progressively short from i-line (365 nm) of a mercury lamp to KrF excimer laser beam (248 nm), and as a positive resist suitable for such short wave exposure, various chemical amplification type positive photoresists have been proposed. Chemical amplification type resists are resists, of which the solubility against a developer of the radiation-irradiated portion is controlled by the catalytic activity of an acid generated by irradiation with a radiation (such as ultraviolet rays, far ultraviolet rays, X-rays or charged particle beams such as electron beams), and it comprises an acid-generating agent and a compound, of which the solubility against an alkali developer increases by an acid catalytic reaction. As a problem specific to such a chemical amplification type positive photoresist, there is a problem in stability due to a delay from exposure to post exposure bake i.e. a problem of a change in the pattern dimension attributable to diffusion of an acid generated if time lapses between the exposure and the post exposure bake. As a technique to solve this problem, JP-A-5-249682 discloses a resist material containing a certain specific resin component, and a specific compound as a suitable acid-generating agent. Specifically, it discloses a resist which contains a polyhydroxystyrene having ethoxyethyl groups and bis(cyclohexylsulfonyl)diazomethane. Further, JP-A-3-223863, JP-A-4-210960, JP-A-4-211258 and U.S. Pat. No. 5,338,641, disclose similar diazomethane type compounds as acid-generating agents.
On the other hand, in the process for preparing semiconductor integrated circuits, it has heretofore been required that resists have good heat resistance. As a result of study, it has been found that such conventional resist materials are inadequate in the heat resistance. If the heat resistance is poor, deformation of a pattern occurs during to the etching process, whereby it tends to be difficult to process lines or the like formed on a substrate precisely to have desired dimensions. In order to prepare highly integrated semiconductor integrated circuits, researches have been conducted to develop a high performance radiation sensitive composition. However, it has been difficult to satisfy various properties such as sensitivity, heat resistance, pattern shape, uniformity of the coating film, and high resolution required from the process side, in good balance.